17 



the immature ones (those contained in about the 600th 

 articulation) having but one (Weinland). The outer 

 covering is very tough, and resists the action of dilute 

 acids, alkalies, and exposure to heat, cold, dampness, 

 or dryness (Aitken). The reason of this is evident at 

 a glance. As the embryo is hatched outside of the 

 body of the parent entozoon, it would be much ex- 

 posed were it not for the resistance offered by its 

 habitation to external influences. 



The number of these eggs in a single proglottis is 

 almost incredible, being counted by thousands. 



Within the covering may be seen the embryo 

 (PI. I. fig. 1), TAir of an i ncn i n breadth (Cobbold), of 

 globular form, and provided with six spines arranged 

 in pairs, one on the top and one on each side, a little 

 anterior to the middle. 



The development of the embryo in the egg appears 

 to take place by segmentation, as may be seen in PL 

 II. fig. 2, after Leuckart (copied from Aitken's " Sci- 

 ence and Practice of Medicine," vol. i.). 



Habitat. These entozoa are found in the small 

 intestine ; but they may grow to such a size as to ex- 

 tend into the large, as in the case quoted from Owen, 

 in the beginning of this chapter. In rare cases, they 

 mount into the stomach. Aubert, of Geneva, has 

 described a tumor of the testicle, caused by a Teenia 

 (Moquin-Tandon). These are very rare, even if not 

 very doubtful, cases, and do not prevent their being 

 considered as inhabitants of the intestine. They are 

 found attached to its mucous membrane by their 



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